The 34th annual Bank of America Chicago Marathon, that started and ended in Grant Park with more than 45,000 runners competing along a 26.2-mile course, wound through 29 Chicago neighborhoods. More than one million spectators lined the course.

Dan HinkelTribune reporter

Firefighter William Caviness was a life-long athlete and veteran marathoner from North Carolina who signed up for the Chicago race aiming to raise $2,000 for burn victims.

He raised nearly $2,500 before the race, and his supporters followed his progress on Facebook as an observer posted an update saying Caviness, a 35-year-old father of two young children, had passed the halfway mark.

Asked what his family felt as the charity effort transformed instantly into a tragedy, his uncle, Bill Caviness of Tennessee, choked back tears and came up with one word.

“Disbelief,” he said.

His death marked the first in the marathon since 2007, organizers said. Caviness' death was the sixth fatality at the event since 1998, according to Tribune archives.

The cause of Caviness' death had not been determined, authorities said. An autopsy is scheduled for Monday.

Caviness, the captain of a fire engine crew in Greensboro, N.C., was running to benefit the International Association of Fire Fighters Burn Foundation, which coordinates fire prevention efforts and supports burn victims. He raised about $2,500 before the race, and donations continued to roll in after news of his death broke Sunday, passing $3,000 by 7 p.m., according to the web site set up to track donations.

“We're just heartbroken,” said Dave Coker, president of the of the city's firefighters' union, said shortly after hearing of Caviness' death. “Will was a competent company officer, a good father, a good husband and he spent his free time raising money for (burn victims.)”

As the race neared, Caviness, known to friends as “Will,” posted on Facebook about training with runs of three, five and 20 miles, sometimes bringing along his baby daughter in a stroller. His wife and brother accompanied him to Chicago as spectators, his uncle said, while his father, Lee, posted encouraging words online as the raced moved on.

“VERY PROUD…WAY TO GO!!!” his father wrote on Facebook.

Family and colleagues remembered him for his sarcasm and sense of humor. Though he was “just one of the guys” around the firehouse, he was also an accomplished athlete, Coker said. Caviness, a Greensboro native, excelled at football and soccer in high school, studied physical therapy in college and had run several marathons, his uncle said.

Coker recalled a half-marathon the two ran together in recent years.

“I don't think I had made the halfway point, and he had already met me coming back,” Coker said. “He was very fit, a tremendous runner.”'

While no one had died in the marathon since 2007, Chicago's marathons and other races have routinely been marred by the deaths of runners, including athletes who appeared physically prepared for the rigors of long-distance running.

The now-infamous 2007 marathon was cut short for the first time in the race's history as temperatures nearing 90 degrees baked downtown streets, turning the race into a chaotic spectacle, with runners dropping out, falling unconscious or vomiting. More than 300 people were taken from the course by ambulance.

One man -- 35-year-old Michigan police officer and experienced distance runner Chad Schieber -- collapsed and died near the 19-mile mark, though Cook County medical officials said his death stemmed from a heart condition, not the heat.